The passport is an electronic record of an individual athlete's biological attributes, developed over time from multiple sample collections. (During the 2008 season, the UCI collected an average of 10 samples each from more than 800 cyclists.) Rather than ordinary spot-testing approaches, which look for unnatural ratios between biological constituents in a single sample or for direct chemical evidence of known doping agents, the passport allows investigators to see the big picture—any deviations from the rider's test-established norm that might result from doping, even if the specific drug or tactic remains unknown.

The UCI has assembled a nine-member panel of independent scientists to evaluate the riders' profiles. Michael Ashenden, a sports scientist with the Science and Industry Against Blood Doping consortium in Australia who sits on the UCI panel, says that each member of the group can examine whatever markers he or she chooses in blood profiles. (The UCI also collects urine samples to track steroids such as testosterone, high levels of which caused 2006 Tour de France champion Floyd Landis to be stripped of his title.)

"I tend to scrutinize reticulocyte [immature red blood cell] values," Ashenden says, "to see if there are any signs of accelerated or decelerated reticulocyte production." An acceleration might point to use of EPO (erythropoietin), a hormone commonly used as a doping agent that boosts red blood cell production, thereby increasing the athlete's ability to deliver oxygen to his or her cells. A decrease in reticulocyte production, he says, could indicate that the athlete just stopped using EPO or recently took a transfusion of stored red blood cells, a process for which the term "blood doping" was coined. "I compare changes in the athlete's values to those I have found in our research that occur with EPO treatment and blood transfusion," Ashenden says.

Even with the benefit of a baseline biological profile for an athlete developed over time, Ashenden says, cautious dopers and drug cheats may remain difficult to detect. "Blatant blood doping is relatively easy to discern from day-to-day fluctuations," he says, whereas a carefully administered treatment regimen is tougher to spot. "Think of it as a signal-to-noise ratio—there is an inherent level of noise (technical error of measurement, day-to-day fluctuations), and only signals greater than this noise level will be apparent."

David Howman, director general of the World Anti-Doping Agency (WADA), which helped develop the biological passport approach, says he is "hopeful and optimistic" that it will make a difference in sports. He refers to the UCI's passport system as a "pilot program" that may pave the way for application across the sporting world. Toward that end, he says, WADA is currently preparing a booklet outlining protocols for instituting bio-passport systems that will be general enough for all sporting federations.

At the same time, Howman emphasizes that the approach is just one more addition to the regulatory arsenal. "I don't think that you should confine yourself to using just one tool," he says. Ashenden agrees that bio-passports will hardly be a panacea for a sport plagued by high-profile doping cases. "Historically, athletes quickly learn to evade new doping tests, and I see no reason why the passport will be any different," he says. "I expect word will begin to spread about how best to minimize their signal level and so escape sanction."

Those clever riders may evade charges but still find their profiles flagged as suspicious, Ashenden says. It remains to be seen how those clues might be used to target other investigative approaches. "Just as we look for new ways to examine what's in the body, we also look at other ways of detecting cheating," Howman says. "They need not be scientific—we can look at who's buying things on the Internet."

Whatever the outcome of the first doping case stemming from the passport program, cycling has at least begun to restore its credibility with the anti-doping movement—WADA has been fiercely critical of the UCI's efforts in the past. "It's a step in the right direction," Howman says. "Cycling has shown that they are serious about it."